稀土掺杂纳米晶在非晶态环境中作为上转换增益介质的深紫外激光性能研究

Upconversion lanthanide-doped fluoride-based nanocrystals, which show supreme upconversion emission efficiency, are commonly synthesized by thermal decomposition, hydrothermal synthesis, and co-precipitation. As these synthesis techniques utilize liquid media to accomplish crystallization process, the colloidal nanocrystals find suitable applications in bio-imaging, bio-detection, cancer therapy, etc. However, upconversion nanocrystals embed in solid media are more suitable than that in liquid media for photonic device applications such as deep ultraviolet (DUV) lasers due to the required harsh operation conditions – high-power excitation, high-energy emission, and high-temperature operation..In this project, we propose the synthesis of fluoride-based lanthanide-doped upconversion DUV (< 300 nm) emission nanocrystals in a glass matrix by melting method. A fluoride-based host lattice, which allows the suppression of concentration quenching, is selected to crystallize in the glass matrix. With suitable control of the annealing temperature and time, surface functionalization can also be realized. This can be done by the formation of an amorphous layer coated on the surface of the nanocrystals to prevent surface quenching. Furthermore, with suitable selection of the dopants, high-efficiency DUV upconversion emission under near-infrared excitation can be obtained. The use of high DUV transparent glass matrix facilitates the fabrication of laser cavities. This, in turn, allows the use of high-excitation scheme and laser phenomenon to enhance upconversion emission efficiency. As a result, these methods alleviate depopulation of intermediate states associated with the non-radiative and radiative processes simultaneously. .Hence, the use of upconversion nanocrystals in glass can realize low-cost and compact DUV diode-pumped solid-state lasers (i.e. like green laser pointers) to satisfy the huge demand of civil and military applications. This also overcomes the problems that most of the intellectual properties related to AlGaN semiconductor technologies (current technology for DUV laser products) owned by foreign companies. Therefore, upconversion nanocrystals in glass can be a new industry standard and platform to achieve low-cost and compact DUV lasers.

利用湿化学方法合成氟化物纳米晶由于其较高的上转换发光效率，在生物成像，生物探测等方面具有广泛应用。在固态环境中的上转换纳米晶，由于其高功率泵浦，高能波段发射及高温操作环境等优势，在深紫外激光器件方面将有更良好的应用前景。.在本项目中，拟采用传统高温熔融法，调控合成在非晶玻璃态环境中生长氟化物纳米晶，使其发射波段位于深紫外区域。选择氟化物作为基质材料及稀土离子作为敏化剂和活化剂，通过调控退火温度及时间，实现纳米晶表面修饰形成同质非晶壳层结构，避免表面缺陷淬灭现象出现。同时，选择高透过性玻璃作为激光谐振腔体，有助于抑制中间能态的辐射以及非辐射过程，保证较高的深紫外上转换发射效率。.因此，选择此材料作为增益介质实现深紫外激光发射，将在民用及军事应用方面具备巨大前景。这将打破国外技术利用AlGaN半导体在深紫外激光器件领域的垄断格局。此项研究成果，将为低成本微型深紫外激光器件的实现提供一条新途径。

随着微电子技术的发展，具有特殊波长、低成本、紧凑多功能等特性的全固态激光器成为研究的热点和难点。特别是UVC深紫外全固态激光器具有波长短、能量集中、分辨率高等优点，在杀菌、光疗、军事等领域具有广泛的应用前景。近年来，稀土掺杂上转换发光具有长发光寿命、反斯托克斯等特性，与传统获得UVC深紫外激光的倍频方案相比有着诸多优势，成为激光领域的新兴方向。..本项目创新性的提出采用原位透射电镜技术揭示稀土(Yb3+，Tm3+/Ho3+/Er3+，Gd3+)掺杂氟化物纳米晶在玻璃透明介质中的生长机理。采用传统高温熔融法，调控合成在非晶玻璃态环境中生长氟化物纳米晶，使其发射波段位于深紫外区域。选择氟化物作为基质材料及稀土离子作为敏化剂和活化剂，通过调控退火温度及时间，实现纳米晶表面修饰形成同质非晶壳层结构，避免表面缺陷淬灭现象出现，抑制中间能态的辐射以及非辐射过程，保证较高的深紫外上转换发射效率。基于此，我们首次研究了原位电镜实时观测Ba2LaF7纳米颗粒在微晶玻璃基体中的生长过程，实现了精准操控纳米晶形貌结构，实现了已经实现了目前波长最短的上转换激光发射，其发射波段位于263nm。因此这一观测对我们在实验过程中优化微晶玻璃的发光特性具有一定的指导意义。该项目的研究成果不仅为制备高效率上转换激光增益材料提供了新思路，并为推动低成本紧凑型UVC激光器件的发展提供一条新途径。